A method for producing sulphuric acid (H2SO4) from gas comprising sulphur dioxide (SO2) is known from the patent SE 510 171. In the method, SO2 is catalytically oxidized to sulphur trioxide (SO3). By contacting SO3 with water (H2O) or aqueous sulphuric acid, the liquid can be strengthened, i.e. its sulphuric acid concentration can be increased. However, in the catalytic oxidization process, the temperature of SO3 is high, typically over 450° C. Moreover both SO3 and H2SO4 are chemically extremely active. Therefore, the materials used in the equipment need to be both heat and corrosion resistant. Such materials are very expensive. Since resources are typically limited, this limits the size of the equipment, whereby, for given resources, the H2SO4 production capacity may remain less than desired.
Moreover, the corrosive nature of sulphuric acid depends on its strength. Sulphuric acid is extremely corrosive in the strength range from about 20 w-% to 85 w-%. However, when the strength is even higher, such as 93 w-% or more, the corrosive nature of H2SO4 is less harsh. This is one reason, why conventional production plants include a strengthening tower configured to strengthen the sulphuric acid to a strength of at least 93 w-%. However, if materials are selected to withstand only substantially pure H2SO4, the process needs to be run in such a way that weaker sulphuric acid is not produced. Otherwise corrosion problems would occur, which could lead to leakage of strong H2SO4 posing health and environmental problems. A process may be hard to run in such a way, whereby such a process is considerably risky. Moreover, in many chemical processes involving sulphuric acid, only weaker sulphuric acid (i.e. aqueous sulphuric acid) is needed, whereby such a strengthening tower is not needed, provided that the system is configured to handle aqueous sulphuric acid. Due to the corrosive nature of aqueous sulphuric acid, suitable materials for the known systems are expensive.
Furthermore, even if corrosion resistant materials are used, the material wear or corrode to some extent during use. Thus, such systems may run to leakages and/or there may be a constant need for maintenance. Maintenance increases the operating costs, and leakages pose safety and environmental risks.